Non-aqueous electrolyte and non-aqueous secondary battery

Abstract

The present disclosure provides a nonaqueous electrolyte containing a nonaqueous solvent and an alkali metal salt. The nonaqueous solvent contains two or more compounds selected from the group consisting of (a) a mononitrile having a molecular weight of 40-70 and (b) a chain ether or a chain carboxylate ester having a molecular weight of 70-120. A total volume fraction of component (a) and component (b) is 0.05-0.80, relative to the total volume of the nonaqueous solvent as 1.

Description

Non-aqueous electrolytes and non-aqueous secondary batteries

[0001] This invention relates to a non-aqueous electrolyte and a non-aqueous secondary battery using the same.

[0002] The applications of lithium-ion batteries are changing amid the global trend of electrification of automobiles. In particular, for automotive batteries, research is being conducted on electrolytes using solvents with low melting points and viscosity to enable stable operation even in low-temperature environments. These low-viscosity solvents also promote good ion diffusion even in batteries with increased electrode thickness and density, making them suitable for achieving high energy density in batteries.

[0003] For example, Patent Documents 1 and 2 report batteries using acetonitrile or esters with low viscosity.

[0004] Japanese Patent Publication No. 2009-146822 Japanese Patent Publication No. 2010-205563

[0005] The purpose of this disclosure is to provide a non-aqueous electrolyte having high ionic conductivity and low volatility.

[0006] Examples of embodiments of the present disclosure are given in the following items [1] to

[18] . [1] A non-aqueous electrolyte comprising a non-aqueous solvent and an alkali metal-containing salt, wherein the non-aqueous solvent contains (a) a mononitrile having a molecular weight of 40 to 70, and (b) two or more compounds selected from the group consisting of a linear ether or a linear carboxylic acid ester having a molecular weight of 70 to 120, and the total volume content of component (a) and component (b) is 0.05 to 0.80 when the total volume of the non-aqueous solvent is 1. [2] The non-aqueous electrolyte according to item 1, wherein the non-aqueous solvent contains two or more compounds selected from the group consisting of (a) mononitriles having a molecular weight of 40 to 70 and (b) linear carboxylic acid esters having a molecular weight of 70 to 120, and the (b) component contains at least one carboxylic acid ester selected from the group consisting of methyl acetate, methyl propionate, ethyl acetate, ethyl propionate, propyl propionate, isopropyl propionate, methyl isobutyrate, and ethyl isobutyrate, and the total volume content of the (a) component and the (b) component is 0.05 to 0.80 when the total volume of the non-aqueous solvent is 1. [3] The non-aqueous electrolyte according to item 1 or 2, wherein the non-aqueous solvent contains at least acetonitrile as the (a) component. [4] The non-aqueous electrolyte according to any one of items 1 to 3, wherein when the total volume of the non-aqueous solvent is 1, the volume content of component (a) and component (b) is Va and Vb respectively, such that 0.05 < Va < 0.4 and 0.05 < Vb < 0.045. [5] The non-aqueous electrolyte according to any one of items 1 to 4, wherein when the total volume of the non-aqueous solvent is 1, the volume content of component (a) and component (b) is Va and Vb respectively, such that 0.04 < 0.3 × Va + 0.09 × Vb.[6] The non-aqueous electrolyte further comprises (c) vinylene carbonate, and the non-aqueous solvent satisfies (1 + Va + Vb × 0.33) × 0.03 ≤ Vc, where Va, Vb, and Vc are the respective volume contents of component (a), component (b), and vinylene carbonate when the total volume of the non-aqueous solvent is 1. [7] The non-aqueous electrolyte according to any one of items 1 to 6, wherein the non-aqueous electrolyte further comprises (c) vinylene carbonate, and the non-aqueous solvent has a volume content of component (a), component (b), and (c) vinylene carbonate, respectively, when the total volume of the non-aqueous solvent is 1, such that Vc ≤ (1 + Va + Vb × 0.33) × 0.061. [8] The non-aqueous electrolyte according to any one of items 1 to 7, wherein the non-aqueous solvent comprises a chain-like carboxylic acid ester having a molecular weight of 80 to 110 as component (b), and the chain-like carboxylic acid ester comprises at least methyl propionate. [9] The non-aqueous electrolyte according to item 1, wherein the non-aqueous solvent contains two or more compounds selected from the group consisting of (a) mononitriles having a molecular weight of 40 to 70 and (b) linear ethers having a molecular weight of 90 to 120, and the total volume content of component (a) and component (b) is 0.05 to 0.80.

[10] The non-aqueous electrolyte according to item 1 or 9, wherein both component (a) and component (b) have a boiling point of 75°C to 130°C at atmospheric pressure.

[11] Both component (a) and component (b) have a density of 0.7 to 0.92 g / cm³ at room temperature. ３ The non-aqueous electrolyte described in any one of items 1, 9, and 10.

[12] Let Ti be the boiling point (°C) of each component of component (a) and component (b), and Vi be the volume content of each component of the non-aqueous solvent, and [Vi × (145 / Ti)] apply to all components of component (a) and component (b). ２ The sum of ] is P: P = Σ[Vi × (145 / Ti)] ２] A non-aqueous electrolyte according to item 1 and any one of items 9 to 11, wherein 0.4 < P < 2.35.

[13] Density (g / cm³) of each component of component (a) and component (b) ３ A non-aqueous electrolyte according to item 1 and any one of items 9 to 12, wherein the Ti is 80 to 95, with ρi being the temperature and Ti being the boiling point (°C), and all of the components with Ti being 80 to 95 have a viscosity of 60 ≤ (Ti × ρi) ≤ 75 and a viscosity at room temperature of less than 0.5 mPa·s.

[14] Density (g / cm³) of each component of component (a) and component (b) ３ A non-aqueous electrolyte according to item 1 and any one of items 9 to 13, wherein Ti is greater than 95 to 130, and all of the components with Ti between 95 and 130 satisfy 75 < (Ti × ρi) ≤ 105.

[15] If Ti is the boiling point (°C) of each component of component (a) and component (b), and Vi is the volume content relative to the non-aqueous solvent, then for all of the components, 0.01 < Vi < (Ti / 135) ２ A non-aqueous electrolyte according to item 1 and any one of items 9 to 14.

[16] The non-aqueous electrolyte according to item 1 and any one of items 9 to 15, wherein the non-aqueous electrolyte comprises acetonitrile as component (a) and 1,2-dimethoxyethane, 1,2-diethoxyethane, or a combination thereof as component (b), and all components other than the non-aqueous solvent have a boiling point of 95°C or higher.

[17] The non-aqueous electrolyte according to any one of items 1 to 16, further comprising vinylene carbonate, ethylene sulfite, or a combination thereof.

[18] A non-aqueous lithium-ion secondary battery comprising a positive electrode having a positive electrode active material layer containing lithium iron phosphate on one or both sides of a positive electrode current collector, a negative electrode having a negative electrode active material layer containing graphite on one or both sides of a negative electrode current collector, a separator, and a non-aqueous electrolyte as described in any one of items 1 to 17.

[0007] According to this disclosure, it is possible to provide a non-aqueous electrolyte having high ionic conductivity and low volatility.

[0008] The embodiments of this disclosure will be described in detail below. Note that numerical ranges indicated using "~" in this specification include the numerical values ​​indicated before and after them. The scope of this disclosure is not limited to the embodiments described herein, and various modifications can be made without departing from the spirit of this disclosure. Furthermore, if multiple upper and lower limits are given for a numerical range, any combination of these upper and lower limits can be used to create a suitable numerical range.

[0009] 《Non-aqueous secondary battery》 The non-aqueous secondary battery of this disclosure is a secondary battery comprising a positive electrode and a negative electrode along with a non-aqueous electrolyte, and may be, for example, a lithium-ion secondary battery. The lithium-ion secondary battery comprises a separator, a positive electrode and a negative electrode sandwiching the separator from both sides, a positive electrode lead (connected to the positive electrode) sandwiching the laminate of these (separator, positive electrode and negative electrode), a negative electrode lead (connected to the negative electrode), and a battery casing housing them. The laminate formed by stacking the positive electrode, separator and negative electrode is impregnated with the non-aqueous electrolyte according to this disclosure.

[0010] 1. Non-aqueous electrolyte In this disclosure, "non-aqueous electrolyte" refers to a non-aqueous electrolyte in which water is 1% by mass or less of the total amount of the non-aqueous electrolyte, and which contains a non-aqueous solvent and an alkali metal-containing salt (also simply referred to as "salt"). The salt preferably contains an alkali metal-containing salt, for example, a lithium salt. It is preferable that the non-aqueous electrolyte contains as little water as possible, but it may contain a very small amount of water as long as it does not hinder the resolution of the problem of this disclosure. The amount of such water is 300 ppm by mass or less, preferably 200 ppm by mass or less, as an amount per unit of the total amount of the non-aqueous electrolyte. As long as the non-aqueous electrolyte has a configuration that achieves the resolution of the problem of this disclosure, other components can be appropriately selected and applied from known non-aqueous electrolyte materials used in lithium-ion batteries.

[0011] 1-1. Non-aqueous solvents In this disclosure, "non-aqueous solvent" refers to the elements of a non-aqueous electrolyte excluding salts and various additives. However, if the non-aqueous electrolyte contains electrode protection additives, "non-aqueous solvent" refers to the elements of the non-aqueous electrolyte excluding salts and additives other than electrode protection additives. Examples of non-aqueous solvents include alcohols such as methanol and ethanol; and aprotic solvents. Among these, aprotic solvents are preferred as non-aqueous solvents. Non-aqueous solvents may contain solvents other than aprotic solvents as long as they do not hinder the resolution of the issues of this disclosure.

[0012] The non-aqueous solvent in the non-aqueous electrolyte of this disclosure preferably contains two or more aprotic solvents with boiling points of 70 to 150°C, more preferably a solvent with a boiling point of 75 to 145°C, and even more preferably a solvent with a boiling point of 80 to 130°C. Here, the boiling point is the value under atmospheric pressure. By containing two or more different components with predetermined boiling points in the non-aqueous solvent, volatility is suppressed by vapor pressure reduction, and if the boiling point of the solvent is 70°C or higher, the effect of volatilization at room temperature is suppressed. Furthermore, from the viewpoint of suppressing vapor generated under high-temperature conditions reached during battery manufacturing and operation, 75°C or higher is more preferable, and 80°C or higher is even more preferable. On the other hand, in aprotic solvents, viscosity tends to increase as the boiling point increases. From the viewpoint of reducing the viscosity of the electrolyte so as not to impair input / output performance or pourability, the viscosity of the solvents contained in the non-aqueous solvent is preferably low, preferably 0.72 mPa·s or less, and more preferably 0.7 mPa·s or less. Furthermore, when the components of the non-aqueous solvent fall within the viscosity range, their boiling point is preferably 150°C or lower, more preferably 145°C or lower, and even more preferably 130°C or lower. By including a solvent with such physical properties, an electrolyte with excellent balance between volatility and viscosity can be obtained, resulting in a non-aqueous electrolyte with high resistance to vacuum processes and high ionic conductivity.

[0013] The non-aqueous solvent in the non-aqueous electrolyte of this disclosure contains two or more solvents selected from the group consisting of (a) mononitriles with a molecular weight of 40 to 70 and (b) linear ethers or linear carboxylic acid esters with a molecular weight of 70 to 120. That is, two or more components may be selected from component (a) alone, two or more components may be selected from component (b) alone, or one or more components may be selected from component (a) and one or more components may be selected from component (b). In this disclosure, "linear" means not having a ring structure. Furthermore, the total volume content of components (a) and (b) combined is 0.05 to 0.8 when the total volume of the non-aqueous solvent is 1. In this way, by including two or more solvent components having specific molecular weights in specific volume content ratios, it is possible to reduce viscosity, increase ionic conductivity, and suppress volatility. The reason for this is not limited to theory, but is presumed to be as follows. In other words, (a) mononitrile has high polarity and low viscosity, which increases the solubility of the electrolyte salt and promotes ion movement, while at the same time, the molecules coordinate with the ions, making them less volatile. Similarly, (b) linear ethers or linear carboxylic acid esters at specific molecular weights also coordinate with ions and become less volatile. Furthermore, when these solvent molecules are mixed, the free solvent molecules that are not coordinated with ions interact with each other, reducing the viscosity of the medium and suppressing volatilization. By including these in the predetermined volume ratios mentioned above, high ionic conductivity and a volatility-suppressing effect can be achieved. From the viewpoint of achieving a higher level of both high ionic conductivity and low volatility, it is preferable to select at least one from component (a), and more preferable to select at least one from component (a) and at least one from component (b).

[0014] In one embodiment, component (b) preferably contains a chain-like carboxylic acid ester with a molecular weight of 70 to 120, and more preferably contains a saturated fatty acid ester as the chain-like carboxylic acid ester. Examples of saturated fatty acid esters include methyl acetate, ethyl acetate, methyl propionate, ethyl propionate, propyl propionate, isopropyl propionate, methyl isobutyrate, and ethyl isobutyrate. Such saturated fatty acid esters possess both high solubility derived from the carbonyl group and moderate volatility and fluidity derived from the lower alkyl group, allowing for precise adjustment of the balance between high ionic conductivity and low volatility. As a result, the electrolyte as a whole can achieve a higher level of both high ionic conductivity and low volatility.

[0015] In one embodiment, it is preferable to include a chain-like ether with a molecular weight of at least 90 to 120 as component (b) from the viewpoint of stability against reduction at the negative electrode and improvement of the electrolyte properties. The reason for this is not limited to theory, but is presumed to be as follows: That is, the chain-like ether as component (b), which has a molecular weight of 90 to 120 than component (a), has a relatively long alkyl chain, so the electron density is easily dispersed, making it stable against electron transfer near the negative electrode and less susceptible to reductive decomposition. In addition, the molecular weight range of 90 to 120 can suppress volatility and prevent an excessive increase in viscosity. As a result, the electrolyte as a whole can achieve a higher level of both high ionic conductivity and low volatility.

[0016] This disclosure is not limited to specific manufacturing methods, battery specifications, etc., but the favorable effects of this disclosure are described below. Organic solvents that achieve both high electrochemical stability and low melting point and viscosity as batteries tend to have low boiling points and are highly volatile. For example, the boiling point of acetonitrile at atmospheric pressure is about 82°C. This is more than 20°C lower than ethyl methyl carbonate, which is commonly used as a non-aqueous electrolyte solvent, indicating a significant difference in volatility. Using highly volatile solvents can raise various concerns in the vacuum process, which is often included in the battery manufacturing process. For example, the vacuum process, when impregnating battery electrodes and separators with electrolyte, extracts gas remaining in the voids of the components while efficiently and uniformly impregnating those voids with electrolyte, affecting the time efficiency and yield of the manufacturing process. Battery specifications that increase energy density tend to have high electrode density and thickness, increasing the need for a vacuum process. However, highly volatile solvent components evaporate under vacuum, and instead of impregnating the voids of the electrodes, they may actually cause drying. In particular, in battery specifications where the amount of electrolyte is minimized to improve energy density and cut costs, the effects of drying due to the vacuum process are expected to be significant. Furthermore, considering the storage of batteries in high-temperature environments, highly volatile electrolytes generate vapor, which may impair performance such as capacity and resistance due to drying of components, and may also cause the battery case to expand due to vapor and solvent decomposition. To solve the volatilization problem under vacuum, for example, if a high-boiling-point non-aqueous solvent is selected to suppress vapor, the viscosity of the liquid tends to increase, which will impair the aforementioned input / output characteristics. Thus, it is presumed that there is a potential trade-off when trying to balance battery performance and processability. Moreover, increasing viscosity impairs the rate of liquid flow and pourability, which may create new process concerns, so the use of high-viscosity solvents does not necessarily lead to a fundamental solution. Therefore, it is important to achieve a suitable balance between viscosity and boiling point or volatility, and since these issues and specific solutions have not been presented in prior literature, it is remarkable that the non-aqueous electrolyte disclosed in this disclosure can solve these problems.

[0017] Component (a) and component (b) each preferably have a boiling point under atmospheric pressure of 75°C or higher and 130°C or lower, more preferably 78°C or higher, and still more preferably 80°C or higher. A solvent having a boiling point of about 75°C to 130°C has an excellent balance between volatility and viscosity, and can ensure appropriate fluidity while maintaining the solubility of the electrolyte salt. Therefore, by combining two or more solvents within this range, it is possible to simultaneously achieve suppression of volatilization and improvement of conductivity.

[0018] In one embodiment, the density of component (a) and component (b) is preferably 0.7 mg / cm ３ to 0.92 mg / cm ３ and more preferably 0.7 mg / cm ３ to 0.915 mg / cm ３ When the density is 0.7 mg / cm ３ or higher, the intermolecular interaction is large, so it is difficult to volatilize and it is difficult to cause fluctuations in the composition during the vacuum process. On the other hand, when it is 0.92 mg / cm ３ or lower, the intermolecular interaction is small and the viscosity tends to be low, promoting the movement of ions. Therefore, a solvent with a density of about 0.70 mg / cm ３ to 0.92 mg / cm ３ can maintain appropriate fluidity while suppressing excessive volatilization because the intermolecular distance and the degree of freedom of molecular motion are appropriately ensured. As a result, the solubility of the electrolyte salt is improved, and the volatility during the vacuum process can be suppressed while ensuring ionic conductivity.

[0019] In one embodiment, when the total volume of the non-aqueous solvent is set to 1, the combined volume content of component (a) and component (b) is preferably 0.8 or less, more preferably 0.75 or less, and particularly preferably 0.7 or less. Furthermore, the lower limit of the total volume content, which can be arbitrarily combined with these upper limits, is preferably 0.05 or more, more preferably 0.1 or more, even more preferably 0.2 or more, and particularly preferably 0.25 or more. When the combined volume content of component (a) and component (b) is 0.05 or more, it is a sufficient proportion in the non-aqueous solvent, and the effect of improving the physical properties of the electrolyte (e.g., low viscosity, improved ionic conductivity, and low volatility) is well exhibited. On the other hand, when the total volume content is 0.8 or less, the balance with other solvent components is good, and the various properties of the non-aqueous electrolyte are excellent. As described above, by preferably including one or more components (a) and (b) that possess a desirable range of molecular weight, boiling point, and volume content, it is possible to achieve both high ionic conductivity and low volatility at a higher level.

[0020] In one embodiment, the non-aqueous solvent preferably contains at least one component as component (a) and / or component (b) having a boiling point (°C) Ti of 80 to 95°C. The component with a boiling point (°C) of 80 to 95°C preferably has a viscosity of 0.5 mPa·s or less at room temperature. Furthermore, the boiling point (°C) Ti and density (mg / cm³) are also specified. ３ The product of ρi (Ti × ρi) is preferably 60 to 75. The inventors considered that the boiling point and density of a compound correlate with volatility and viscosity, respectively, and that Ti × ρi is a good indicator for considering the balance between boiling point and density, and thus focused on this parameter. As described above, they found that with respect to components (a) and (b) having specific molecular weights, the viscosity and volatility tend to decrease when a solvent component in which Ti × ρi is within the above specific range is included. In this case, the total volume content of components (a) and (b) is preferably 0.7 or less, more preferably 0.6 or less, even more preferably 0.5 or less, and also preferably 0.05 or more, preferably 0.1 or more, and even more preferably 0.2 or more, when the total amount of the non-aqueous solvent is considered as 1.

[0021] In one embodiment, the non-aqueous solvent preferably contains at least one component as component (a) and / or component (b) having a boiling point (°C) Ti greater than 95 to 130°C. Furthermore, the viscosity of the component at room temperature is preferably 0.72 mPa·s or less, more preferably 0.71 mPa·s or less, and even more preferably 0.7 mPa·s or less. In addition, the component with a Ti greater than 95 to 130°C has a boiling point (°C) Ti and density (mg / cm³). ３ The product of ρi (Ti × ρi) is preferably 75 to 105. For the same reasons as above, the inventors focused on Ti × ρi and found that by including a solvent component in which such Ti × ρi is within the above specific range, volatility can be further suppressed while viscosity can also be sufficiently suppressed. In this case, the total volume content of component (a) and component (b) is preferably 0.8 or less, more preferably 0.7 or less, preferably 0.05 or more, more preferably 0.1 or more, and even more preferably 0.2 or more, when the total amount of the non-aqueous solvent is considered to be 1.

[0022] To maintain a favorable balance of viscosity and volatility in the non-aqueous electrolyte, the volume content of each component (a) and (b), when the total volume of the non-aqueous solvent is set to 1, is preferably appropriate according to the physical properties of each component. When the boiling point (°C) of each component (a) and (b) at atmospheric pressure is Ti, the volume content of each component is (Ti / 135). ２ Preferably, the following is true: (Ti / 145) ２ Preferably, the following conditions apply: (Ti / 150) ２ The following is more preferable. The inventors, noting that the volatility in a vacuum process differs for each boiling point of non-aqueous solvents, weighted each material according to its boiling point and investigated what the upper limit of the volume content of each component could be in order to maintain a balance between viscosity and volatility, leading them to focus on this parameter. That is, low-boiling point components contribute significantly to volatility even in small amounts, while high-boiling point components do not impair compositional stability even when included in relatively large amounts. Therefore, the upper limit of the volume content of each component is determined by a parameter (Ti / constant) based on its boiling point. ２By scaling in this way, the allowable amounts of low-boiling-point and high-boiling-point components can be rationally determined while taking into account their contributions. We found that by including the components in a constant volume content determined for each boiling point in this way, higher vacuum process resistance and lower viscosity can be achieved. The lower limit of the volume content of each component of component (a) and component (b) may preferably be 0.01 or higher, more preferably 0.05 or higher, and even more preferably 0.07 or higher.

[0023] On the other hand, since the non-aqueous solvent of the non-aqueous electrolyte according to this disclosure may be used in combination with various components (a) and (b), the overall properties of the electrolyte, such as viscosity, conductivity, volatility, and high-temperature stability, are determined by the final mixed composition. When multiple types of solvents with different boiling points are included, in order to sufficiently reduce volatility in the final mixed composition, increase conductivity, and suppress decomposition reactions, the mixing ratio parameter P is calculated by the following formula, where Vi is the volume content of each component (a) and (b) when the total volume of the non-aqueous solvent is set to 1: P = Σ[Vi × (145 / Ti)] ２ Regarding ], P is preferably 0.4 or higher, more preferably 0.6 or higher, and even more preferably 0.8 or higher. Furthermore, the upper limit of P, which can be arbitrarily combined with these lower limits, is preferably 2.35 or lower, more preferably 2.1 or lower, even more preferably 1.8 or lower, and particularly preferably 1.5 or lower. However, Σ[Vi × (145 / Ti)] ２ ] is the sum of all components included as component (a) and component (b). The inventors defined the upper limit Vmax of the volume content of each material as the boiling point parameter "(145 / Ti) ２ When set individually in ", the sum of Vi / Vmax across the entire material (Σ[Vi × (145 / Ti)] ２We believe that the following parameter serves as a good indicator for considering the balance of the volume content of each material, and thus we have focused on this parameter. That is, even a small amount of a low-boiling-point solvent contributes significantly to volatility, while a large amount of a high-boiling-point solvent has a relatively small impact on volatility. For this reason, rather than simply summing the volume content Vi, we have chosen to use a parameter (145 / Ti) based on the boiling point to adequately reflect the differences in volatility of each solvent. ２ By correcting for this and defining a normalized index using this correction, the balance of viscosity, volatility, and conductivity of the entire mixed composition can be appropriately evaluated. Furthermore, we found that when the electrolyte composition P falls within this range, there is a good balance between viscosity and volatility, and a tendency to obtain electrolyte characteristics with excellent high-temperature stability while achieving high levels of both conductivity and volatility.

[0024] (a) The component is preferably an aliphatic mononitrile represented by the general formula: R-CN, where R is an aliphatic group having 1 to 5 carbon atoms, for example, an alkyl group. Specifically, the alkyl mononitrile having an alkyl group preferably contains one or more compounds selected from acetonitrile, propionitrile, butyronitrile, and isobutyronitrile.

[0025] (b) The chain ether of component is preferably of the general formula: RO-(CH ２ ) ｎThe component is a dialkoxyalkane represented by -OR', where R and R' are each independently an aliphatic group having 1 to 5 carbon atoms, such as an alkyl group, and n is preferably an integer from 1 to 5. More preferably, 1,2-dialkoxyethane, specifically 1,2-dimethoxyethane and 1,2-diethoxyethane are included. The chain-like carboxylic acid ester of component (b) is preferably a fatty acid ester represented by the general formula: R-C(O)O-R', where R and R' are each independently an aliphatic group having 1 to 5 carbon atoms, such as an alkyl group. Examples include methyl acetate, ethyl acetate, methyl propionate, ethyl propionate, propyl propionate, isopropyl propionate, methyl isobutyrate, and ethyl isobutyrate. The molecular weight of component (b) is 70 to 120, more preferably 80 to 110. Component (b) with a molecular weight of 80 to 110 is more preferably methyl propionate.

[0026] From the viewpoint of effectively reducing viscosity and volatility, it is particularly preferable to include acetonitrile as component (a). When acetonitrile is included, its high dielectric constant interacts with the salt in the electrolyte, further suppressing volatility and promoting the dissolution of the salt. In addition, the inclusion of acetonitrile can improve the rapid charging characteristics of non-aqueous secondary batteries. In constant current (CC)-constant voltage (CV) charging of non-aqueous secondary batteries, the capacity per unit time during the CC charging period is greater than the charge capacity per unit time during the CV charging period. When acetonitrile is used as the non-aqueous solvent in the non-aqueous electrolyte, the area in which CC charging can be performed can be enlarged (the CC charging time can be extended), and the charging current can also be increased, so the time from the start of charging to the fully charged state of the non-aqueous secondary battery can be significantly shortened. When acetonitrile is included as component (a), acetonitrile is highly reactive, and there is a risk that a reduction reaction on the negative electrode surface may lead to a decrease in battery capacity or gas generation, but the inclusion of a chain-like carboxylic acid ester as component (b) tends to increase stability. Nitrile compounds and linear carboxylic acid esters are compounds that can be reduced at the reaction potential of a graphite anode. Mixing them within a predetermined range tends to stabilize battery characteristics while exhibiting high ionic conductivity. Furthermore, from the viewpoint of effectively reducing viscosity, reactivity, and volatility, it is preferable to include acetonitrile as component (a) and a combination of one or more linear carboxylic acid esters selected from the group consisting of ethyl propionate, ethyl acetate, and methyl propionate as component (b), and more preferably to include at least methyl propionate. By mixing these substances, good physical properties of a non-aqueous electrolyte can be achieved, and battery performance at high temperatures can be stabilized without impairing conductivity while reducing volatility. In addition, performance at low temperatures can also be improved by reducing viscosity. Furthermore, from the viewpoint of more effectively reducing viscosity and volatility, it is preferable to include acetonitrile as component (a) and / or to include at least one selected from the group consisting of 1,2-dimethoxyethane and 1,2-diethoxyethane as component (b).It is preferable to include either or both of 1,2-dimethoxyethane and 1,2-diethoxyethane, as this increases stability against reduction reactions. These substances satisfy the aforementioned solvent properties of boiling point, density, and molecular weight, possess a good balance of boiling point and viscosity, and can suppress volatility without impairing battery performance.

[0027] In one embodiment, when the total volume of the non-aqueous solvent is taken as 1, the volume contents of components (a) and (b) are Va and Vb, respectively, preferably 0.05 < Va < 0.4 and 0.05 < Vb < 0.045. Here, if there are two or more types of components (a) and (b), Va is the total volume content of component (a) and Vb is the total volume content of component (b). When the volume contents of components (a) and (b) are within the above range, a higher level of balance between viscosity and volatility can be achieved, increasing ionic conductivity while further enhancing stability in high-temperature environments. In one embodiment, it is more preferable that Va and Vb satisfy the following relationship: 0.04 < 0.3 × Va + 0.09 × Vb. This parameter was chosen based on the viscosity and reactivity of nitrile compounds and ether or linear carboxylic acid ester compounds. By ensuring that the volume content ratios Va and Vb of each component satisfy the above relationship, the contributions of component (a) and component (b) can be reflected in a balanced manner. As a result, it was found that high ionic conductivity can be achieved while simultaneously reducing viscosity and suppressing volatility in vacuum processes, and furthermore, higher stability can be obtained even in high-temperature environments.

[0028] To suppress the electrochemical reductive decomposition of the mononitrile compounds mentioned above, it is preferable that the non-aqueous electrolyte further contains electrode protective additives for forming a protective film on the electrodes.

[0029] Examples of aprotic solvents included as non-aqueous solvents other than components (a) and (b) include cyclic carbonates, fluoroethylene carbonates, lactones, organic compounds having sulfur atoms, chain-like fluorinated carbonates, cyclic ethers, mononitriles other than (a), alkoxy-substituted nitriles, dinitriles, cyclic nitriles, short-chain fatty acid esters, chain-like ethers other than (b), fluorinated ethers, ketones, and compounds in which some or all of the H atoms of the aprotic solvent are substituted with halogen atoms.

[0030] To suppress the electrochemical reductive decomposition of (a) nitrile compounds and (b) components, particularly saturated fatty acid esters, which are components of the non-aqueous solvent, adding a negative electrode SEI (Solid Electrolyte Interface) forming additive to the non-aqueous electrolyte stabilizes the charge and discharge rate of the battery when used in a non-aqueous secondary battery. Examples of negative electrode SEI forming additives include vinylene carbonate, fluoroethylene carbonate, and ethylene sulfite, with vinylene carbonate, ethylene sulfite, or a combination thereof being particularly preferred. Vinylene carbonate can effectively prevent nitrile compounds and saturated fatty acid ester compounds from directly contacting the negative electrode and undergoing reductive decomposition. The non-aqueous electrolyte preferably contains at least acetonitrile as component (a) and more preferably further contains (c) vinylene carbonate.

[0031] It is more preferable that the SEI-forming additive is included in an amount necessary depending on the amounts of component (a) and component (b). When the total volume of the non-aqueous solvent is 1, and the volume composition ratios of component (a), component (b), and (c) vinylene carbonate contained are Va, Vb, and Vc, it is preferable that (1 + Va + Vb × 0.33) × 0.03 ≤ Vc. The inventors considered that the preferred amount of additive can be determined based on the correlation between the reaction rate of the additive and the reaction rate of each solvent component, and thus focused on the parameter "1 + Va + Vb × 0.33". They found that when the amount of additive Vc is in the range of "(1 + Va + Vb × 0.33) × 0.03" or greater relative to Va and Vb, the decomposition of the solvent is effectively suppressed and the stability of the electrolyte in a high-temperature environment is improved.

[0032] When SEI-forming additives are used, there is a risk of gas generation and increased resistance due to their reductive decomposition reaction. On the other hand, when acetonitrile is included as component (a) and saturated fatty acid ester as component (b), the solvent component reacts with vinylene carbonate (c), which tends to prevent gas generation and increased resistance associated with the reaction of the SEI additive. When the total volume of the non-aqueous solvent is set to 1, and the volume composition ratios of the contained components (a), (b), and (c) vinylene carbonate are Va, Vb, and Vc, it is preferable that Vc ≤ (1 + Va + Vb × 0.33) × 0.061. For the same reasons as above, the inventors focused on the parameter "(1 + Va + Vb × 0.33)" and found that when the amount of additive Vc is within the range of "(1 + Va + Vb × 0.33) × 0.061" relative to Va and Vb, gas generation and resistance increase of the additive in a high-temperature environment are suppressed, and the properties of the electrolyte are improved.

[0033] When the non-aqueous solvent contains vinylene carbonate as a cyclic carbonate and ethylene sulfite as an organic compound containing sulfur atoms, the non-aqueous electrolyte can operate the battery at a high current density when used in a non-aqueous secondary battery.

[0034] Because vinylene carbonate-derived negative electrode protective coatings have high resistance, they tend to lead to performance degradation during rapid charging and in low-temperature environments, as well as battery swelling due to gas generation during decomposition. Ethylene sulfite has a lower lowest unoccupied orbital (LUMO) level compared to other oxygen-containing sulfur compounds, and can be reductively decomposed at a lower potential than vinylene carbonate to form a negative electrode protective coating. This makes it possible to reduce the amount of vinylene carbonate added and solve the problems associated with vinylene carbonate-derived negative electrode protective coatings. Furthermore, ethylene sulfite-derived negative electrode protective coatings have low resistance over a wide temperature range, and promote the formation of a more durable negative electrode SEI (Solid Electrolyte Interface), thereby providing a non-aqueous electrolyte and non-aqueous secondary battery that can operate stably at high current densities.

[0035] From the viewpoint of suppressing an increase in internal resistance, it is preferable that the total content of vinylene carbonate and ethylene sulfite in the non-aqueous electrolyte in this disclosure be 0.1% by volume or more and less than 15% by volume relative to the total amount of the non-aqueous solvent.

[0036] Examples of cyclic carbonates include ethylene carbonate, propylene carbonate, 1,2-butylene carbonate, trans-2,3-butylene carbonate, cis-2,3-butylene carbonate, 1,2-pentylene carbonate, trans-2,3-pentylene carbonate, cis-2,3-pentylene carbonate, vinylene carbonate (VC), 4,5-dimethylvinylene carbonate, and vinylethylene carbonate.

[0037] Examples of fluoroethylene carbonates include 4-fluoro-1,3-dioxolan-2-one, 4,4-difluoro-1,3-dioxolan-2-one, cis-4,5-difluoro-1,3-dioxolan-2-one, trans-4,5-difluoro-1,3-dioxolan-2-one, 4,4,5-trifluoro-1,3-dioxolan-2-one, 4,4,5,5-tetrafluoro-1,3-dioxolan-2-one, and 4,4,5-trifluoro-5-methyl-1,3-dioxolan-2-one.

[0038] Examples of lactones include γ-butyrolactone, α-methyl-γ-butyrolactone, γ-valerolactone, γ-caprolactone, δ-valerolactone, δ-caprolactone, and ε-caprolactone.

[0039] Examples of organic compounds containing sulfur atoms include ethylene sulfite, propylene sulfite, butylene sulfite, pentene sulfite, sulfolane, 3-sulfolene, 3-methylsulfolane, 1,3-propanesultone, 1,4-butanesultone, 1-propene-1,3-sultone, dimethyl sulfoxide, tetramethylene sulfoxide, and ethylene glycol sulfite.

[0040] Examples of chain-like carbonates include ethyl methyl carbonate, dimethyl carbonate, diethyl carbonate, methyl propyl carbonate, methyl isopropyl carbonate, dipropyl carbonate, methyl butyl carbonate, dibutyl carbonate, ethyl propyl carbonate, and diisobutyl carbonate.

[0041] Examples of cyclic ethers include tetrahydrofuran, 2-methyltetrahydrofuran, 1,4-dioxane, and 1,3-dioxane.

[0042] Other mononitriles besides acetonitrile include, for example, propionitrile, butyronitrile, valeronitrile, benzonitrile, and acrylonitrile.

[0043] Examples of alkoxy-substituted nitriles include methoxyacetonitrile and 3-methoxypropionitrile.

[0044] Examples of dinitriles include malononitrile, succinonitrile, glutalonitrile, adiponitrile, 1,4-dicyanoheptane, 1,5-dicyanopentane, 1,6-dicyanohexane, 1,7-dicyanoheptane, 2,6-dicyanoheptane, 1,8-dicyanooctane, 2,7-dicyanooctane, 1,9-dicyanononane, 2,8-dicyanononane, 1,10-dicyanodecane, 1,6-dicyanodecane, and 2,4-dimethylglutalonitrile.

[0045] An example of a cyclic nitrile is benzonitrile.

[0046] Examples of short-chain fatty acid esters include methyl acetate, methyl propionate, methyl isobutyrate, methyl butyrate, methyl isovalerate, methyl valerate, methyl pivalate, methyl hydroangelicaate, methyl caproate, ethyl acetate, ethyl propionate, ethyl isobutyrate, ethyl butyrate, ethyl isovalerate, ethyl valerate, ethyl pivalate, ethyl hydroangelicaate, ethyl caproate, propyl acetate, propyl propionate, propyl isobutyrate, propyl butyrate, propyl isovalerate, propyl valerate, propyl pivalate, propyl hydroangelicaate, propyl caproate, isopropyl acetate, isopropyl propionate, isopropyl isobutyrate, isopropyl butyrate, isopropyl isovalerate, isopropyl valerate, isopropyl pivalate Examples include isopropyl hydroangelicate, isopropyl caproate, butyl acetate, butyl propionate, butyl isobutyrate, butyl butyrate, butyl isovalerate, butyl valerate, butyl pivalate, butyl hydroangelicate, butyl caproate, isobutyl acetate, isobutyl propionate, isobutyrate, isobutyrate, isobutyl isovalerate, isobutyl valerate, isobutyl pivalate, isobutyl hydroangelicate, isobutyl caproate, tert-butyl acetate, tert-butyl propionate, tert-butyl isobutyrate, tert-butyl butyrate, tert-butyl isovalerate, tert-butyl valerate, tert-butyl pivalate, tert-butyl hydroangelicate, and tert-butyl caproate.

[0047] Examples of linear ethers include dimethoxyethane, diethyl ether, 1,3-dioxolane, diglyme, triglyme, and tetraglyme.

[0048] Examples of fluorinated ethers include Rf ２０ -OR ２１ (In the formula, Rf ２０ represents an alkyl group containing a fluorine atom, and R ７ This represents a monovalent organic group that may contain a fluorine atom.

[0049] Examples of ketones include acetone, methyl ethyl ketone, and methyl isobutyl ketone.

[0050] Examples of compounds in which some or all of the H atoms in an aprotic solvent are substituted with halogen atoms include compounds in which the halogen atom is fluorine.

[0051] Examples of fluorinated chain carbonates include methyltrifluoroethyl carbonate, trifluorodimethyl carbonate, trifluorodiethyl carbonate, trifluoroethylmethyl carbonate, methyl 2,2-difluoroethyl carbonate, methyl 2,2,2-trifluoroethyl carbonate, and methyl 2,2,3,3-tetrafluoropropyl carbonate. The above fluorinated chain carbonates are represented by the following general formula: R １ -OC(O)OR ２ {In the formula, R １ and R ２ CH ３ ,CH ２ CH ３ ,CH ２ CH ２ CH ３ , CH (CH ３ ) ２ , and CH ２ Rf ３ At least one selected from the group consisting of Rf ３ is an alkyl group having 1 to 3 carbon atoms in which at least one fluorine atom replaces a hydrogen atom, and R １ and / or R ２ It contains at least one fluorine atom. This can be expressed as}.

[0052] Furthermore, examples of fluorinated short-chain fatty acid esters include fluorinated short-chain fatty acid esters such as 2,2-difluoroethyl acetate, 2,2,2-trifluoroethyl acetate, and 2,2,3,3-tetrafluoropropyl acetate. Fluorinated short-chain fatty acid esters are represented by the following general formula: R １０ -C(O)O-R １１ {In the formula, R １０ CH ３ ,CH ２ CH ３ ,CH ２ CH２ CH ３ , CH (CH ３ ) ２ CF ３ CF ２ H, CFH ２ CF ２ Rf １２ , CFHRf １２ , and CH ２ Rf １３ At least one selected from the group consisting of R １１ CH ３ ,CH ２ CH ３ ,CH ２ CH ２ CH ３ , CH (CH ３ ) ２ , and CH ２ Rf １３ At least one selected from the group consisting of Rf １２ Rf is a C1-C3 alkyl group in which at least one fluorine atom may substitute for a hydrogen atom. １３ is an alkyl group having 1 to 3 carbon atoms in which at least one fluorine atom replaces a hydrogen atom, and R １０ and / or R １１ It contains at least one fluorine atom, R １０ ga CF ２ If H, R １１ CH ３ It is not.} It can be expressed as}.

[0053] It is preferable to use two or more aprotic solvents in combination. In addition to the component (a) and the component (b), the non-aqueous solvent of the present disclosure preferably further contains one or more selected from the group consisting of cyclic carbonates and chain carbonates from the viewpoint of improving the electrical stability of the non-aqueous electrolyte. Cyclic carbonates and chain carbonates alone are difficult to achieve a balance between viscosity and volatility. However, when blended and used in combination with a predetermined amount of the component (a) and the component (b), it is possible to achieve a balance between viscosity and volatility while improving electrical stability and volatility. For example, it is more preferable to use a cyclic carbonate and a chain carbonate having a boiling point of 100 ° C or higher in combination from the viewpoints of electrical stability and volatility.

[0054] When using a cyclic carbonate other than vinylene carbonate, it is particularly preferable that such a cyclic carbonate contains ethylene carbonate and / or fluoroethylene carbonate.

[0055] 1-2. Electrolyte salt The salt contained in the non-aqueous electrolyte of the present disclosure only needs to contain an electrolyte salt and is not particularly limited. For example, in a non-aqueous electrolyte for a lithium ion secondary battery, it is preferable to contain a lithium salt. Specifically, LiPF ６ and may contain a lithium-containing imide salt, but is not limited thereto.

[0056] The lithium-containing imide salt is LiN(SO ２ C ｍ F ２ｍ＋１ )( [Wherein, m is an integer of 0 to 8]) and is a lithium salt represented by, specifically, LiN(SO ２ F)( [Wherein, m is an integer of 0 to 8]) and is a lithium salt represented by, specifically, LiN(SO ２ F)( [Wherein, m is an integer of 0 to 8]) and is a lithium salt represented by, specifically, LiN(SO ２ ), and LiN(SO ２ CF ３ )( [Wherein, m is an integer of 0 to 8]) and is a lithium salt represented by, specifically, LiN(SO ２ ). It is preferable to contain at least one of these imide salts. It may contain only one of these imide salts or both. Or, it may contain an imide salt other than these imide salts.

[0057] When acetonitrile is included in the non-aqueous solvent, since the saturated concentration of the lithium-containing imide salt with respect to acetonitrile is high, it is preferable to include the lithium-containing imide salt because it can suppress the association and precipitation of the lithium salt and acetonitrile at low temperatures. Also, from the viewpoint of the ion supply amount, it is preferable that the content of the lithium-containing imide salt is 0.5 mol or more and 3 mol or less per 1 L of the non-aqueous solvent. LiN(SO ２ F) ２ , and LiN(SO ２ CF ３ ) ２ According to an acetonitrile-containing non-aqueous electrolyte solution containing at least one of them, it is possible to effectively suppress a reduction in ionic conductivity in a low-temperature range such as -10 °C or -30 °C, and excellent low-temperature characteristics can be obtained. Thus, by limiting the content, it is also possible to more effectively suppress an increase in resistance during high-temperature heating. When the electrolyte salt is contained in the non-aqueous electrolyte solution at a predetermined concentration or more, the volatility is further suppressed by the electrostatic interaction between the dissociated cations and anions and the non-aqueous solvent molecules. On the other hand, when the electrolyte salt is contained at a predetermined concentration or less, the viscosity of the non-aqueous electrolyte solution becomes low and the ionic conductivity becomes high, so it is preferable to keep its concentration below a certain level. From this viewpoint, the total concentration of the electrolyte salt is preferably 0.5 to 3 mol per 1 L of the non-aqueous solvent, more preferably 0.8 to 2.5 mol, and even more preferably 0.9 to 2 mol.

[0058] As the lithium salt, it may further contain a fluorine-containing inorganic lithium salt other than LiPF ６ , for example, LiBF ４ , LiAsF ６ , Li ２ SiF ６ , LiSbF ６ , Li ２ B １２ F ｂ H １２－ｂThe formula may include fluorine-containing inorganic lithium salts such as [wherein b is an integer from 0 to 3]. "Inorganic lithium salt" refers to a lithium salt that does not contain carbon atoms as anions and is soluble in acetonitrile. "Fluorine-containing inorganic lithium salt" refers to a lithium salt that does not contain carbon atoms as anions, contains fluorine atoms as anions, and is soluble in acetonitrile. Fluorine-containing inorganic lithium salts are excellent in that they form a passive film on the surface of the metal foil, which is the positive electrode current collector, and suppress corrosion of the positive electrode current collector. These fluorine-containing inorganic lithium salts can be used individually or in combination of two or more. As the fluorine-containing inorganic lithium salt, a compound that is a double salt of LiF and a Lewis acid is desirable, and among these, a fluorine-containing inorganic lithium salt having a phosphorus atom is more preferable because it readily releases free fluorine atoms. A typical fluorine-containing inorganic lithium salt dissolves into PF ６ LiPF that emits anions ６ Therefore, when a fluorine-containing inorganic lithium salt containing boron atoms is used as the fluorine-containing inorganic lithium salt, it is preferable because it becomes easier to capture excess free acid components that may cause battery degradation, and from this viewpoint, LiBF ４ That is particularly preferable.

[0059] There are no particular restrictions on the content of the fluorine-containing inorganic lithium salt in the non-aqueous electrolyte of this disclosure, but it is preferably 0.01 mol or more, more preferably 0.02 mol or more, and even more preferably 0.03 mol or more per liter of non-aqueous solvent. When the content of the fluorine-containing inorganic lithium salt is within the above range of 0.01 mol or more, the ionic conductivity tends to increase, and high power characteristics can be exhibited. Furthermore, the content of the fluorine-containing inorganic lithium salt is preferably less than 1.5 mol, more preferably less than 0.5 mol, and even more preferably less than 0.1 mol per liter of non-aqueous solvent. When the content of the fluorine-containing inorganic lithium salt is within the above range of less than 1.5 mol, the ionic conductivity increases, high power characteristics can be exhibited, and the decrease in ionic conductivity due to viscosity increase at low temperatures tends to be suppressed. This tends to improve the high-temperature cycle characteristics and other battery characteristics of the non-aqueous secondary battery while maintaining the excellent performance of the non-aqueous electrolyte.

[0060] The non-aqueous electrolyte of this disclosure may further contain an organolithium salt. An "organolithium salt" means a lithium salt that contains a carbon atom as an anion and is soluble in a non-aqueous solvent.

[0061] Examples of organolithium salts include organolithium salts having an oxalic acid group. Specific examples of organolithium salts having an oxalic acid group include, for example, LiB(C) ２ O ４ ) ２ LiBF ２ (C ２ O ４ ), LiPF ４ (C ２ O ４ ), and LiPF ２ (C ２ O ４ ) ２ Examples include organolithium salts represented by each of the following, among which LiB(C) ２ O ４ ) ２ and LiBF ２ (C ２ O ４At least one lithium salt selected from the lithium salts represented by ) is preferred. It is even more preferable to use one or more of these together with a fluorine-containing inorganic lithium salt. This organolithium salt having an oxalic acid group may be added to a non-aqueous electrolyte or incorporated into the negative electrode (negative electrode active material layer).

[0062] From the viewpoint of ensuring better effects from its use, the amount of organolithium salt having an oxalic acid group added to a non-aqueous electrolyte is preferably 0.005 moles or more, more preferably 0.02 moles or more, and even more preferably 0.05 moles or more, per liter of non-aqueous solvent in the non-aqueous electrolyte. However, if the amount of organolithium salt having an oxalic acid group in the non-aqueous electrolyte is too large, precipitation may occur. Therefore, the amount of organolithium salt having an oxalic acid group added to a non-aqueous electrolyte is preferably less than 1.0 mole, more preferably less than 0.5 moles, and even more preferably less than 0.2 moles, per liter of non-aqueous solvent in the non-aqueous electrolyte.

[0063] Organolithium salts containing oxalic acid groups are known to be poorly soluble in low-polarity organic solvents, particularly in linear carbonates. Organolithium salts containing oxalic acid groups may contain trace amounts of lithium oxalate, and furthermore, when mixed as a non-aqueous electrolyte, they may react with trace amounts of water contained in other raw materials, generating a new white precipitate of lithium oxalate. Therefore, the lithium oxalate content in the non-aqueous electrolyte of this disclosure is not particularly limited, but is preferably 0 to 500 ppm.

[0064] In addition to the lithium salts listed above, other lithium salts commonly used in non-aqueous secondary batteries may be added as auxiliary lithium salts in this disclosure. Specific examples of other lithium salts include, for example, LiClO ４ LiAlO ４ LiAlCl ４ LiB １０ Cl １０ , inorganic lithium salts that do not contain fluorine atoms as anions, such as chloroborane Li; LiCF ３ SO ３LiCF ３ CO ２ Li ２ C ２ F ４ (SO ３ ) ２ LiC (CF ３ SO ２ ) ３ LiC ｎ F （２ｎ＋１） SO ３ {In the formula, n≧2}, lower aliphatic carboxylic acid Li, tetraphenylborate Li, LiB (C ３ O ４ H ２ ) ２ Organic lithium salts such as LiPF ５ (CF ３ LiPF such as ) ｎ (C ｐ F ２ｐ＋１ ) ６－ｎ An organolithium salt represented by the formula [wherein n is an integer from 1 to 5 and p is an integer from 1 to 8]: LiBF ３ (CF ３ LiBF (Lithium Bacteria) ｑ (C ｓ F ２ｓ＋１ ) ４－ｑ Examples include organolithium salts represented by the formula [wherein q is an integer from 1 to 3 and s is an integer from 1 to 8], and lithium salts bonded to polyvalent anions. Preferably, the lithium salt is the following formula (a): LiC(SO ２ R Ａ ) (SO ２ R Ｂ ) (SO ２ R Ｃ ) (a) {wherein, R Ａ , R Ｂ , and R Ｃ These may be the same or different, and represent a perfluoroalkyl group having 1 to 8 carbon atoms.}, Formula (b) below: LiN(SO ２ OR Ｄ ) (SO ２ OR Ｅ ) (b) {wherein, R Ｄ , and R ＥThese may be the same or different from each other, and represent a perfluoroalkyl group having 1 to 8 carbon atoms.}, and the following formula (c): LiN(SO ２ R Ｆ ) (SO ２ OR Ｇ ) (c) {wherein, R Ｆ , and R Ｇ These may be the same or different from each other, and represent a perfluoroalkyl group having 1 to 8 carbon atoms. Examples include organolithium salts represented by each of these. One or more of these can be used together with a fluorine-containing inorganic lithium salt.

[0065] 1-3. Additives The non-aqueous electrolyte according to this disclosure may contain additives in addition to the non-aqueous solvent and electrolyte salt described above. Preferably, the non-aqueous electrolyte further contains electrode protection additives, such as vinylene carbonate, ethylene sulfite, or a combination thereof.

[0066] The non-aqueous electrolyte in this disclosure may contain vinylene carbonate as an additive. The vinylene carbonate undergoes a reduction reaction on the surface of the negative electrode active material to form a film, which can prevent the continuous reduction reaction of other solvents. Its content is preferably 1% by weight or more, preferably 2% by weight or more, and more preferably 4% by weight or more, based on the total amount of the non-aqueous electrolyte. It is also preferably 10% by weight or less, and more preferably 7% by weight or less.

[0067] The non-aqueous electrolyte in this disclosure may contain ethylene sulfite as an additive. Ethylene sulfite can cause a reduction reaction on the surface of the negative electrode active material to form a film, preventing continuous reduction reactions of other solvents. When ethylene sulfite is included as an additive, it is preferable to use vinylene carbonate in combination. Using these additives in combination tends to cause a film to form more rapidly on the surface of the negative electrode active material. The ethylene sulfite content is preferably 0.1% by weight or more, more preferably 0.5% by weight or more, and even more preferably 1% by weight or more, based on the total amount of the non-aqueous electrolyte. Furthermore, it is preferably 6% by weight or less, and even more preferably 5% by weight or less.

[0068] There are no particular restrictions on the electrode protection additive as long as it does not hinder the resolution of the issues described herein, and it may substantially overlap with the substance that plays the role of a solvent for dissolving lithium salts (i.e., the non-aqueous solvent described above). The electrode protection additive is preferably a substance that contributes to improving the performance of the non-aqueous electrolyte and the non-aqueous secondary battery in this disclosure, but it also includes substances that do not directly participate in the electrochemical reaction.

[0069] Other specific examples of electrode protection additives include, for example, 4-fluoro-1,3-dioxolan-2-one, 4,4-difluoro-1,3-dioxolan-2-one, cis-4,5-difluoro-1,3-dioxolan-2-one, trans-4,5-difluoro-1,3-dioxolan-2-one, 4,4,5-trifluoro-1,3-dioxolan-2-one, and 4,4,5,5-tetrafluoro-1,3-dioxolan-2-one. Fluoroethylene carbonates represented by xollan-2-one and 4,4,5-trifluoro-5-methyl-1,3-dioxollan-2-one; unsaturated bond-containing cyclic carbonates represented by 4,5-dimethylvinylene carbonate and vinylethylene carbonate; γ-butyrolactone, γ-valerolactone, γ-caprolactone, δ-valerolactone, δ-caprolactone, and ε-caprolactone Examples include representative lactones; cyclic ethers represented by 1,4-dioxane; cyclic sulfur compounds represented by propylene sulfite, butylene sulfite, pentene sulfite, sulfolane, 3-sulfolene, 3-methylsulfolane, 1,3-propanesultone, 1,4-butanesultone, 1-propene-1,3-sultone, and tetramethylene sulfoxide; chain acid anhydrides represented by acetic anhydride, propionic anhydride, and benzoic anhydride; cyclic acid anhydrides represented by malonic anhydride, succinic anhydride, glutaric anhydride, maleic anhydride, phthalic anhydride, 1,2-cyclohexanedicarboxylic anhydride, 2,3-naphthalenedicarboxylic anhydride, or naphthalene-1,4,5,8-tetracarboxylic dianhydride; and mixed acid anhydrides with structures formed by the dehydration condensation of two different carboxylic acids, or different types of acids such as a carboxylic acid and a sulfonic acid. These can be used individually or in combination of two or more.

[0070] There are no particular restrictions on the content of the electrode protection additive in the non-aqueous electrolyte, but the content of the electrode protection additive relative to the total amount of the non-aqueous solvent is preferably 0.1 to 30% by volume, more preferably 0.3 to 15% by volume, and even more preferably 0.5 to 4% by volume.

[0071] The higher the content of the electrode protection additive, the more the degradation of the non-aqueous electrolyte is suppressed. However, the lower the content of the electrode protection additive, the better the high-power characteristics of the non-aqueous secondary battery in low-temperature environments. Therefore, by adjusting the content of the electrode protection additive within the above range, it is possible to maximize the excellent performance based on the high ionic conductivity of the non-aqueous electrolyte without impairing the basic functions of the non-aqueous secondary battery. By preparing the non-aqueous electrolyte with such a composition, it is possible to further improve the cycle performance, high-power performance in low-temperature environments, and other battery characteristics of the non-aqueous secondary battery. From the above viewpoint, it is preferable that the electrode protection additive be contained in an amount necessary according to the total content of components (a) and (b) contained in the non-aqueous electrolyte. This makes it possible to effectively improve battery performance while preventing the reductive decomposition rate of the solvent. The total weight content of the electrode protection additive is preferably 0.05 Mab or more, more preferably 0.1 Mab or more, and even more preferably 0.15 Mab or more, relative to the total weight content (Mab) of component (a) and component (b) in the non-aqueous solvent. In particular, it is preferable to include vinylene carbonate as the electrode protection additive, and its weight content is preferably 0.05 Mab or more, more preferably 0.1 Mab or more, and even more preferably 0.15 Mab or more.

[0072] For the purpose of improving the charge-discharge cycle characteristics of non-aqueous secondary batteries, high-temperature storage capabilities, and safety (e.g., overcharge prevention), the non-aqueous electrolyte contains, for example, sulfonic acid esters, diphenyl disulfide, cyclohexylbenzene, biphenyl, fluorobenzene, tert-butylbenzene, phosphate esters [ethyl diethyl phosphonoacetate (EDPA): (C ２ H ５ O) ２ (P=O)-CH ２(C=O)OC ２ H ５ Tris(trifluoroethyl) phosphate (TFEP): (CF ３ CH ２ O) ３ P=O, triphenyl phosphate (TPP):(C ６ H ５ O) ３ P = O: (CH ２ =CHCH ２ O) ３ The product may also contain optional additives selected from P=O, triallyl phosphate, nitrogen-containing cyclic compounds without steric hindrance around lone pairs of electrons (such as pyridine, 1-methyl-1H-benzotriazole, 1-methylpyrazole, etc.), and derivatives of these compounds. Phosphate esters, in particular, are effective in suppressing side reactions during storage.

[0073] The content of other optional additives is calculated as a mass percentage of the total mass of all components constituting the non-aqueous electrolyte. There are no particular restrictions on the content of other optional additives, but it is preferably in the range of 0.01% to 10% by mass, more preferably 0.02% to 5% by mass, and even more preferably 0.05% to 3% by mass, relative to the total amount of the non-aqueous electrolyte. By adjusting the content of other optional additives to the above range, it is possible to add even better battery characteristics without impairing the basic functions of the non-aqueous secondary battery.

[0074] 2. Positive electrode and positive electrode current collector The positive electrode is composed of a positive electrode active material layer made from a positive electrode mixture and a positive electrode current collector. The positive electrode is not particularly limited as long as it acts as the positive electrode of a non-aqueous secondary battery, and may be a known one. The positive electrode in this disclosure preferably contains a lithium-containing compound that contains Fe, and more preferably contains nickel (Ni) in a relatively high proportion.

[0075] The positive electrode active material layer is arranged on one or both sides of the positive electrode current collector, contains positive electrode active material, and preferably further contains a conductive additive and a binder as needed.

[0076] The positive electrode active material layer preferably contains a material capable of intercalating and releasing lithium ions as the positive electrode active material. Using such a material tends to yield high voltage and high energy density, which is therefore preferable.

[0077] The positive electrode active material contained in the positive electrode active material layer is the following general formula (1): Li ｗ MPO ４ .....(1) {In the formula, M represents one or more transition metal elements, and the value of w is determined by the charge / discharge state of the battery, and represents a number from 0 to 1.2, preferably a number from 0.05 to 1.10.} A phosphate metal compound containing lithium and a transition metal element represented by the following general formula (2): Li ｐ Ni ｑ Co ｒ Mn ｓ M ｔ O ｕ .....(2) {In the formula, M is at least one metal selected from the group consisting of aluminum (Al), tin (Sn), indium (In), iron (Fe), vanadium (V), copper (Cu), magnesium (Mg), titanium (Ti), zinc (Zn), molybdenum (Mo), zirconium (Zr), strontium (Sr), and barium (Ba), and is in the range of 0 < p < 1.3, 0 < q < 1.2, 0 < r < 1.2, 0 ≤ s < 0.5, 0 ≤ t < 0.3, 0.7 ≤ q + r + s + t ≤ 1.2, 1.8 < u < 2.2, and p is a value determined by the charge / discharge state of the battery.} At least one Li-containing metal oxide selected from the lithium (Li)-containing metal oxides represented by the formula is preferred.

[0078] A specific example of a positive electrode active material is, for example, Li ｗ FePO ４ Lithium iron phosphate, or LiCoO ２ Lithium cobalt oxide, such as LiMnO, is a representative example. ２ LiMn ２ O ４ , and Li ２ Mn ２ O４ Lithium manganese oxides, such as LiNiO, are representative of this type of oxide. ２ Lithium nickel oxide, such as LiNi, is a representative example. １／３ Co １／３ Mn １／３ O ２ LiNi ０．５ Co ０．２ Mn ０．３ O ２ LiNi ０．８ Co ０．２ O ２ Li, represented by ｚ MO ２ Examples include lithium-containing composite metal oxides represented by the formula (wherein M includes at least one transition metal element selected from the group consisting of Ni, Mn, and Co, and represents two or more metal elements selected from the group consisting of Ni, Mn, Co, Al, and Mg, and z represents a number greater than 0.9 and less than 1.2).

[0079] In particular, when the Ni content ratio q of the Li-containing metal oxide represented by general formula (2) is 0.5 < q < 1.2, it is preferable because both a reduction in the amount of rare metal Co used and an increase in energy density can be achieved. For example, LiNi is a good cathode active material. ０．６ Co ０．２ Mn ０．２ O ２ LiNi ０．７５ Co ０．１５ Mn ０．１５ O ２ LiNi ０．８ Co ０．１ Mn ０．１ O ２ LiNi ０．８５ Co ０．０７５ Mn ０．０７５ O ２ LiNi ０．８ Co ０．１５ Al ０．０５ O ２ LiNi ０．８１ Co ０．１ Al ０．０９ O ２ LiNi ０．８５ Co ０．１ Al ０．０５ O ２Examples include lithium-containing composite metal oxides such as those mentioned above.

[0080] On the other hand, the higher the Ni content in the positive electrode active material layer, the more likely degradation is to occur at low voltages. The positive electrode active material of Li-containing metal oxide represented by general formula (2) inherently contains active sites that cause oxidative degradation of non-aqueous electrolytes, but these active sites can unintentionally consume compounds added to protect the negative electrode on the positive electrode side. Acid anhydrides, in particular, tend to be susceptible to this effect.

[0081] Furthermore, these additive decomposition products incorporated into and deposited on the positive electrode side not only increase the internal resistance of non-aqueous secondary batteries but also accelerate the degradation of lithium salts. Moreover, the protection of the negative electrode surface, which was the original purpose, becomes insufficient. In order to deactivate the active sites that essentially cause oxidative degradation of non-aqueous electrolytes, the coexistence of components that control Jahn-Teller strain or act as neutralizers is important. For this reason, it is preferable that the positive electrode active material contains at least one metal selected from the group consisting of Al, Sn, In, Fe, V, Cu, Mg, Ti, Zn, Mo, Zr, Sr, and Ba.

[0082] For similar reasons, it is preferable that the surface of the positive electrode active material is coated with a compound containing at least one metal element selected from the group consisting of Zr, Ti, Al, and Nb. It is even more preferable that the surface of the positive electrode active material is coated with an oxide containing at least one metal element selected from the group consisting of Zr, Ti, Al, and Nb. Furthermore, it is preferable that the surface of the positive electrode active material is coated with ZrO ２ , TiO ２ Al ２ O ３ NbO ３ , and LiNbo ２ It is particularly preferable that the material be coated with at least one oxide selected from the group consisting of the following, because this does not hinder the permeation of lithium ions.

[0083] The positive electrode active material may be a lithium-containing compound other than the Li-containing metal oxide represented by formulas (1) and (2), and is not particularly limited as long as it contains lithium. Examples of such lithium-containing compounds include composite oxides containing lithium and a transition metal element, metal chalcogenides containing lithium, and metal silicate compounds containing lithium and a transition metal element. From the viewpoint of obtaining a higher voltage, a metal phosphate compound containing lithium and at least one transition metal element selected from the group consisting of Co, Ni, Mn, Fe, Cu, Zn, Cr, V, and Ti is particularly preferred as the lithium-containing compound. More specifically, a lithium-containing compound of the following formula (Xa): Li ｖ M Ｉ D ２ ... (Xa) {wherein D represents a chalcogen element, M Ｉ represents one or more transition metal elements, and the value of v is determined by the charge / discharge state of the battery, and represents a number between 0.05 and 1.10.}, and the following formula (Xb): Li ｔ M ＩＩ ｕ SiO ４ ・・・・・・(Xb) {In the formula, M ＩＩ Compounds represented by each of the following are examples:} where represents one or more transition metal elements, the value of t is determined by the charge / discharge state of the battery and is a number between 0.05 and 1.10, and u is a number between 0 and 2.

[0084] The lithium-containing compound represented by formula (Xa) above has a layered structure, and the compounds represented by formula (1) and formula (Xb) above have an olivine structure. These lithium-containing compounds may be modified in such ways as to stabilize the structure, by substituting some of the transition metal elements with Al, Mg, or other transition metal elements, incorporating these metal elements into the grain boundaries, substituting some of the oxygen atoms with fluorine atoms, or coating at least a portion of the surface of the positive electrode active material with another positive electrode active material.

[0085] In this disclosure, the positive electrode active material may be any lithium-containing compound as described above, or other positive electrode active materials may be used in combination with the lithium-containing compound.

[0086] Other positive electrode active materials include, for example, metal oxides or metal chalcogenides having tunnel and layered structures; sulfur; conductive polymers, etc. Examples of metal oxides or metal chalcogenides having tunnel and layered structures include MnO ２ FeO ２ FeS ２ , V ２ O ５ , V ６ O １３ , TiO ２ TiS ２ MoS ２ , and NbSe ２ Examples of conductive polymers include oxides, sulfides, and selenides of metals other than lithium. Examples of conductive polymers include polyaniline, polythiophene, polyacetylene, and polypyrrole.

[0087] The other positive electrode active materials mentioned above can be used individually or in combination of two or more, and there are no particular restrictions. However, it is preferable that the positive electrode active material layer contains at least one transition metal element selected from Ni, Mn, and Co, in order to enable reversible and stable intercalation and release of lithium ions and to achieve high energy density.

[0088] When a lithium-containing compound and another positive electrode active material are used in combination as the positive electrode active material, the ratio of the lithium-containing compound to the total positive electrode active material is preferably 80% by mass or more, and more preferably 85% by mass or more.

[0089] Examples of conductive additives include graphite, acetylene black, carbon black such as Ketjenblack, and carbon fibers. The content ratio of the conductive additive is preferably 10 parts by mass or less, and more preferably 1 to 5 parts by mass, per 100 parts by mass of positive electrode active material.

[0090] Examples of binders include polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), polyacrylic acid, styrene-butadiene rubber, and fluororubber. The binder content is preferably 10 parts by mass or less, and more preferably 0.5 to 8 parts by mass, per 100 parts by mass of positive electrode active material.

[0091] The positive electrode active material layer is formed by dispersing a slurry containing a positive electrode mixture, which is obtained by mixing the positive electrode active material with a conductive additive and a binder as needed, in a solvent, onto a positive electrode current collector, drying (solvent removal), and pressing as needed. There are no particular restrictions on the solvent used, and conventionally known solvents can be used. Examples include N-methyl-2-pyrrolidone, dimethylformamide, dimethylacetamide, and water.

[0092] The positive electrode current collector is made of a metal foil such as aluminum foil, nickel foil, or stainless steel foil. The positive electrode current collector may have a carbon coating on its surface or may be processed into a mesh shape. The thickness of the positive electrode current collector is preferably 5 to 40 μm, more preferably 7 to 35 μm, and even more preferably 9 to 30 μm.

[0093] 3. Negative electrode and negative electrode current collector The negative electrode consists of a negative electrode active material layer made from a negative electrode mixture and a negative electrode current collector. The negative electrode can function as the negative electrode of a non-aqueous secondary battery.

[0094] The negative electrode active material layer is preferably arranged on one or both sides of the negative electrode current collector, contains the negative electrode active material, and optionally contains a conductive additive and a binder. The non-aqueous lithium-ion secondary battery according to this disclosure is preferably structured to allow injection of a non-aqueous electrolyte in an amount of X mass% relative to the mass of the negative electrode active material, as described above.

[0095] Examples of negative electrode active materials include amorphous carbon (hard carbon), graphite (e.g., artificial graphite, natural graphite), pyrolytic carbon, coke, glassy carbon, calcined organic polymer compounds, mesocarbon microbeads, carbon fibers, activated carbon, carbon colloids, and carbon black, as well as metallic lithium, metal oxides, metal nitrides, lithium alloys, tin alloys, silicon alloys, intermetallic compounds, organic compounds, inorganic compounds, metal complexes, and organic polymer compounds. The negative electrode active material can be used alone or in combination of two or more. From the viewpoint of the application of the non-aqueous electrolyte according to this disclosure, graphite is preferred as the negative electrode active material.

[0096] From the perspective of increasing the battery voltage, lithium ions are used as the negative electrode active material in the negative electrode active material, resulting in a 0.4V vs. Li / Li ratio. ＋ It is preferable to include a material that can absorb at a lower potential.

[0097] Examples of conductive additives include graphite, acetylene black, carbon black such as Ketjenblack, and carbon fibers. The content ratio of the conductive additive is preferably 20 parts by mass or less, and more preferably 0.1 to 10 parts by mass, per 100 parts by mass of the negative electrode active material.

[0098] Examples of binders include carboxymethylcellulose, PVDF, PTFE, polyacrylic acid, and fluororubber. Diene rubbers, such as styrene-butadiene rubber, are also acceptable. The binder content is preferably 10 parts by mass or less, and more preferably 0.5 to 8 parts by mass, per 100 parts by mass of the negative electrode active material.

[0099] The negative electrode active material layer is formed by dispersing a negative electrode mixture, which is a mixture of the negative electrode active material and, if necessary, a conductive additive and a binder, in a solvent, onto a negative electrode current collector, drying (solvent removal), and pressing as necessary. There are no particular restrictions on the solvent used, and conventionally known solvents can be used. Examples include N-methyl-2-pyrrolidone, dimethylformamide, dimethylacetamide, and water.

[0100] The negative electrode current collector is made of a metal foil such as copper foil, nickel foil, or stainless steel foil. The negative electrode current collector may also have a carbon coating on its surface or be processed into a mesh shape. The thickness of the negative electrode current collector is preferably 5 to 40 μm, more preferably 6 to 35 μm, and even more preferably 7 to 30 μm.

[0101] 4. Separator In the non-aqueous secondary battery of this disclosure, it is preferable to provide a separator between the positive electrode and the negative electrode from the viewpoint of providing safety such as preventing short circuits and shutdown of the positive and negative electrodes. The separator is not limited, but may be the same as that provided in known non-aqueous secondary batteries, and a thin insulating film with high ion permeability and excellent mechanical strength is preferred. Examples of separators include woven fabrics, non-woven fabrics, and microporous membranes made of synthetic resins, and among these, microporous membranes made of synthetic resins are preferred.

[0102] Suitable examples of synthetic resin microporous membranes include polyolefin-based microporous membranes, such as those containing polyethylene or polypropylene as the main component, or those containing both of these polyolefins. Examples of nonwoven fabrics include heat-resistant resin porous membranes made of glass, ceramic, polyolefin, polyester, polyamide, liquid crystal polyester, aramid, etc.

[0103] The separator may have a structure consisting of a single layer or multiple layers of one type of microporous membrane, or it may have two or more types of microporous membranes laminated together. The separator may also have a structure consisting of a single layer or multiple layers of a mixed resin material obtained by melt-kneading two or more types of resin materials.

[0104] For the purpose of imparting functionality, inorganic particles may be present on the surface or inside the separator, and other organic layers may be further coated or laminated. Furthermore, a cross-linked structure may be included. These methods may be combined as needed to enhance the safety performance of non-aqueous secondary batteries.

[0105] By using such a separator, it is possible to achieve the excellent input / output characteristics and low self-discharge characteristics that are particularly required for lithium-ion batteries used in the high-power applications mentioned above.

[0106] While there are no particular limitations on the film thickness of the microporous membrane that can be used as a separator, it is preferably 1 μm or more from the viewpoint of film strength and preferably 500 μm or less from the viewpoint of permeability. From the viewpoint of use in high-power applications where the heat generation is relatively high and self-discharge characteristics better than conventional are required, such as in safety tests, and from the viewpoint of windability in large battery winding machines, the film thickness of the microporous membrane is preferably 5 μm to 30 μm, and more preferably 10 μm to 25 μm. Furthermore, when prioritizing both short-circuit resistance and output performance, the film thickness of the microporous membrane is more preferably 15 μm to 25 μm, but when prioritizing both high energy density and output performance, it is more preferably 10 μm to less than 15 μm.

[0107] The porosity of a microporous membrane usable as a separator is preferably 30% to 90%, more preferably 35% to 80%, and even more preferably 40% to 70%, from the viewpoint of keeping up with the rapid movement of lithium ions at high power output. Furthermore, if the priority is on improving power output performance while ensuring safety, a porosity of 50% to 70% is particularly preferred for the microporous membrane, and if the importance is on balancing short-circuit resistance and power output performance, a porosity of 40% to less than 50% is particularly preferred.

[0108] For microporous membranes usable as separators, the air permeability should be 1 second / 100 cm, considering the balance between film thickness and porosity. ３ More than 400 seconds / 100cm ３ The following is preferable: 100 seconds / 100 cm ３ More than 350 / 100cm ３ The following is preferable. Furthermore, if prioritizing both short-circuit resistance and output performance, the air permeability of the microporous membrane should be 150 seconds / 100 cm. ３ Over 350 seconds / 100cm ３ The following is particularly preferable, and when prioritizing improved output performance while ensuring safety, 100 / 100 cm ３seconds or more 150 seconds / 100cm ３ A value less than 10 mS / cm is particularly preferred. On the other hand, when a non-aqueous electrolyte with low ionic conductivity is combined with a separator within the above range, the rate of lithium ion migration is limited not by the separator structure but by the ionic conductivity of the non-aqueous electrolyte, and the expected input / output characteristics tend not to be obtained. For this reason, the ionic conductivity of the non-aqueous electrolyte is preferably 10 mS / cm or higher, more preferably 15 mS / cm, and even more preferably 20 mS / cm. However, the film thickness, air permeability, and porosity of the separator, as well as the ionic conductivity of the non-aqueous electrolyte, are not limited to the above examples.

[0109] 5. Battery casing The configuration of the battery casing for a non-aqueous secondary battery is not particularly limited, but for example, either a battery can or a laminate film casing can be used. As the battery can, for example, metal cans made of steel, stainless steel, aluminum, or clad material, such as rectangular, rectangular tube, cylindrical, elliptical, flat, coin-shaped, or button-shaped cans can be used. As the laminate film casing, for example, a laminate film consisting of a three-layer structure of heat-melt resin / metal film / resin can be used.

[0110] The laminate film casing can be used by stacking two sheets with the heat-melt resin side facing inward, or by folding the film so that the heat-melt resin side faces inward, and sealing the ends with heat seal. When using the laminate film casing, the positive electrode current collector may be connected to the positive electrode lead (or positive electrode terminal and lead tab connected to the positive electrode terminal), and the negative electrode current collector may be connected to the negative electrode lead (or negative electrode terminal and lead tab connected to the negative electrode terminal). In this case, the laminate film casing may be sealed with the ends of the positive electrode lead and negative electrode lead (or lead tab connected to the positive electrode terminal and negative electrode terminal, respectively) extended to the outside of the casing.

[0111] 《Method for Manufacturing a Non-Aqueous Secondary Battery》 The non-aqueous secondary battery in this disclosure is manufactured by a known method using the above-mentioned non-aqueous electrolyte, a positive electrode having a positive electrode active material layer on one or both sides of a current collector, a negative electrode having a negative electrode active material layer on one or both sides of a current collector, a battery casing, and a separator as needed.

[0112] First, a laminate is formed consisting of a positive electrode, a negative electrode, and a separator as needed. For example: a configuration in which a wound laminate is formed by winding long positive and negative electrodes in a laminated state with the long separator interposed between the positive and negative electrodes; a configuration in which a laminate is formed by alternately stacking positive electrode sheets and negative electrode sheets, obtained by cutting the positive and negative electrodes into multiple sheets having a certain area and shape, with a separator sheet in between; a configuration in which a laminate is formed by folding a long separator in a zigzag pattern and alternately inserting positive electrode sheets and negative electrode sheets between the zigzag-folded separators; and so on.

[0113] Next, the laminate described above is housed in a battery casing (battery case), the non-aqueous electrolyte according to this disclosure is poured into the battery case, and the laminate is immersed in the non-aqueous electrolyte and sealed to produce the non-aqueous secondary battery according to this disclosure. On the other hand, if the laminate is only impregnated with the non-aqueous electrolyte, air bubbles contained inside the laminate may not be removed, and the impregnation may not proceed efficiently. Therefore, it is preferable to remove air bubbles by pouring the non-aqueous electrolyte into the battery case, then leaving it in a reduced-pressure vacuum environment before sealing, and performing a vacuum impregnation process (or simply a vacuum process).

[0114] Alternatively, a non-aqueous secondary battery can be manufactured by first creating a gel-like electrolyte membrane by impregnating a polymer material substrate with a non-aqueous electrolyte, then forming a laminated structure using a sheet-like positive electrode, negative electrode, electrolyte membrane, and separators as needed, and finally housing it in a battery casing.

[0115] Furthermore, if the electrode arrangement is designed such that there is an overlap between the outer edge of the negative electrode active material layer and the outer edge of the positive electrode active material layer, or if there is a section of the negative electrode active material layer that is too narrow in the non-opposing portion, misalignment of the electrodes may occur during battery assembly, potentially degrading the charge-discharge cycle characteristics of the non-aqueous secondary battery. Therefore, it is preferable to fix the electrode positions in advance using tapes such as polyimide tape, polyphenylene sulfide tape, or polypropylene (PP) tape, or adhesives, when using the electrode body for the non-aqueous secondary battery.

[0116] Due to the high ionic conductivity of non-aqueous electrolytes, lithium ions released from the positive electrode during the initial charge of a non-aqueous secondary battery may diffuse throughout the negative electrode. In non-aqueous secondary batteries, it is common practice to have a larger negative electrode active material layer than the positive electrode active material layer. However, if lithium ions diffuse and are intercalated in areas of the negative electrode active material layer that do not face the positive electrode active material layer, these lithium ions will remain in the negative electrode without being released during the initial discharge. As a result, the contribution of these unreleased lithium ions becomes irreversible capacity, potentially reducing capacity efficiency.

[0117] On the other hand, if the area of ​​the positive electrode active material layer is larger than that of the negative electrode active material layer, or if the areas are the same, current concentration is more likely to occur at the edges of the negative electrode active material layer during charging, making it easier for lithium dendrites to form.

[0118] For the reasons stated above, there are no particular restrictions on the ratio of the total area of ​​the negative electrode active material layer to the area of ​​the portion where the positive electrode active material layer and the negative electrode active material layer face each other, but it is preferably greater than 1.0 and less than 1.1, more preferably greater than 1.002 and less than 1.09, even more preferably greater than 1.005 and less than 1.08, and particularly preferably greater than 1.01 and less than 1.08. In a non-aqueous secondary battery using a non-aqueous electrolyte containing acetonitrile, the initial charge-discharge efficiency can be improved by reducing the ratio of the total area of ​​the negative electrode active material layer to the area of ​​the portion where the positive electrode active material layer and the negative electrode active material layer face each other.

[0119] Reducing the ratio of the total area of ​​the negative electrode active material layer to the area of ​​the portion where the positive electrode active material layer and the negative electrode active material layer face each other means limiting the proportion of the negative electrode active material layer that does not face the positive electrode active material layer. This makes it possible to minimize the amount of lithium ions absorbed by the portion of the negative electrode active material layer that does not face the positive electrode active material layer (i.e., the amount of lithium ions that are not released from the negative electrode during the first discharge and become irreversible capacity) from the lithium ions released from the positive electrode during the first charge. Therefore, by designing the ratio of the total area of ​​the negative electrode active material layer to the area of ​​the portion where the positive electrode active material layer and the negative electrode active material layer face each other within the above range, it is possible to improve the load characteristics of the battery by using acetonitrile, increase the initial charge-discharge efficiency of the battery, and further suppress the formation of lithium dendrites.

[0120] Non-aqueous secondary batteries can function as batteries after the initial charge, but they are stabilized by the decomposition of a portion of the non-aqueous electrolyte during the initial charge. There are no particular restrictions on the method of initial charging, but it is preferable to perform the initial charge at 0.001 to 0.3C, more preferably at 0.002 to 0.25C, and even more preferably at 0.003 to 0.2C. It is also preferable for the initial charge to be performed via constant voltage charging in between. By setting a long voltage range in which the lithium salt is involved in the electrochemical reaction, a stable and robust SEI is formed on the electrode (negative electrode) surface, which has the effect of suppressing the increase in internal resistance. In addition, the reaction products are not firmly fixed only on the negative electrode, but also have a good effect on components other than the negative electrode, such as the positive electrode and separator, in some way. For this reason, it is very effective to perform the initial charge considering the electrochemical reaction of the lithium salt dissolved in the non-aqueous electrolyte.

[0121] The non-aqueous secondary battery in this disclosure can also be used as a battery pack in which multiple non-aqueous secondary batteries are connected in series or in parallel. From the viewpoint of managing the charge and discharge state of the battery pack, the operating voltage range per battery is preferably 2 to 5V.

[0122] While embodiments of this disclosure have been described above, this disclosure is not limited to the embodiments described above. This disclosure can be modified in various ways without departing from its essence.

[0123] The present disclosure will be further described below with reference to examples. The present disclosure is not limited to these examples.

[0124] Examples 1-8 and Comparative Examples 1-6 (1) Preparation of non-aqueous electrolyte Under an inert atmosphere, various non-aqueous solvents containing component (a) and component (b) are mixed in predetermined volume composition ratios to form lithium bis(fluorosulfonyl)imide (LiFSI) and LiPF ６ The two components were dissolved in 1 M and 0.3 M solutions, respectively, and a predetermined amount (weight %) of the additive was added to the total volume of the electrolyte to prepare a non-aqueous electrolyte. Here, the abbreviations for the non-aqueous solvent, lithium salt, and additive have the following meanings, and for components (a) and (b), the boiling point (°C) at atmospheric pressure and the density (g / cm³) of the solvent at room temperature are indicated. ３ The following was done: After preparation, an ion conductivity meter CM-41X (product name) and an ion conductivity measurement cell CT-58101B (product name) manufactured by DKK Corporation were inserted into the container containing the electrolyte, and the ion conductivity of the electrolyte at 25°C was measured. In addition, the detection terminal of a vibrating viscometer VM-10A (product name) manufactured by Sekonic Corporation was inserted into the container containing the solvent, and the viscosity of components (a) and (b) at 25°C was measured. (Electrolyte salt) LiFSI: Lithium bis(fluorosulfonyl)imide LiPF ６ : Lithium hexafluorophosphate (non-aqueous solvent (a)) AcN: Acetonitrile (boiling point 82°C, density 0.77 g / cm³) ３ Ti × ρi = 63.14, viscosity at room temperature 0.35 mPa·s, (Ti / 135) ２ =0.37, (Ti / 145) ２ =0.32, (Ti / 150) ２ = 0.30) iBN: Isobutyronitrile (boiling point 107°C, density 0.78 g / cm³) ３ Ti × ρi = 83.46, viscosity at room temperature 0.63 mPa·s, (Ti / 135) ２ =0.62, (Ti / 145)２ =0.55, (Ti / 150) ２ = 0.51) (Non-aqueous solvent (b)) DME: 1,2-dimethoxyethane (boiling point 84°C, density 0.86 g / cm³) ３ Ti × ρi = 72.24, viscosity at room temperature 0.43 mPa·s, (Ti / 135) ２ =0.39, (Ti / 145) ２ =0.34, (Ti / 150) ２ = 0.31) DEE: 1,2-diethoxyethane (boiling point 121°C, density 0.85 g / cm³) ３ Ti × ρi = 102.85, viscosity at room temperature 0.65 mPa·s, (Ti / 135) ２ =0.80, (Ti / 145) ２ =0.70, (Ti / 150) ２ = 0.65) MA: Methyl acetate (boiling point 57°C, density 0.93 g / cm³) ３ Ti × ρi = 53.01, viscosity at room temperature 0.37 mPa·s, (Ti / 135) ２ =0.18, (Ti / 145) ２ =0.16, (Ti / 150) ２ = 0.14) EA: Ethyl acetate (boiling point 77°C, density 0.90 g / cm³) ３ Ti × ρi = 69.3, viscosity at room temperature 0.43 mPa·s, (Ti / 135) ２ =0.33, (Ti / 145) ２ =0.28, (Ti / 150) ２ = 0.26) MP: Methyl propionate (boiling point 80°C, density 0.91 g / cm³) ３ Ti × ρi = 72.8, viscosity at room temperature 0.44 mPa·s, (Ti / 135) ２ =0.54, (Ti / 145) ２ =0.30, (Ti / 150) ２ = 0.28) EP: Ethyl propionate (boiling point 99°C, density 0.89 g / cm³) ３ Ti × ρi = 88.11, viscosity at room temperature 0.56 mPa·s, (Ti / 135) ２ =0.36, (Ti / 145) ２ =0.47, (Ti / 150) ２= 0.44) (Other than non-aqueous solvents (a) and (b)) EMC: Ethyl methyl carbonate EC: Ethylene carbonate VC: Vinylen carbonate (Additives) ES: Ethylene sulfite

[0125] (2) Fabrication of non-aqueous secondary batteries (2-1) Fabrication of positive electrode (A) LiFePO as positive electrode active material ４ (B) Acetylene black powder as a conductive additive and (C) polyvinylidene fluoride (PVDF) as a binder were mixed in a ratio of 90:2:8 to obtain a positive electrode mixture.

[0126] N-methyl-2-pyrrolidone was added as a solvent to the obtained positive electrode mixture and mixed further to prepare a positive electrode mixture-containing slurry. A slurry containing this positive electrode mixture was applied at a basis weight of 20 mg / cm² to one or both sides of a 15 μm thick aluminum foil, which would serve as the positive electrode current collector. ２ The material was applied while adjusting the temperature, and the solvent was dried and removed in a hot air drying oven. After that, the density of the positive electrode active material layer was reduced to 2.2 g / cm³ using a roll press. ３ By rolling the material to obtain a positive electrode consisting of a positive electrode active material layer and a positive electrode current collector, the leads were welded together. Subsequently, the positive electrode was obtained by vacuum drying at 120°C for more than 12 hours.

[0127] (2-2) Preparation of the negative electrode (a) As the negative electrode active material, graphite, (b) a conductive additive, (c) carboxymethylcellulose, and (d) styrene-butadiene rubber were mixed in a mass ratio of 96:1:1.5:1.5 to obtain a negative electrode mixture.

[0128] Water was added as a solvent to the obtained negative electrode mixture and mixed further to prepare a slurry containing the negative electrode mixture. A basis weight of 10 mg / cm² was applied to one or both sides of a 10 μm thick copper foil that would serve as the negative electrode current collector. ２ The material was applied in this manner, and the solvent was dried and removed in a hot air drying oven. Subsequently, the density of the negative electrode active material layer was reduced to 1.5 g / cm³ using a roll press. ３ The material was rolled to obtain a negative electrode consisting of a negative electrode active material layer and a negative electrode current collector, and the leads were welded. Then, the negative electrode was vacuum dried at 80°C for more than 12 hours.

[0129] (3) Fabrication and evaluation of non-aqueous secondary batteries (3-1) Fabrication of laminate sheet type non-aqueous secondary battery and evaluation of vacuum process resistance In a dry room with a dew point temperature of -80 to -20°C, the leaded positive electrode and leaded negative electrode, after cutting, were stacked in layers of eight sheets with polyethylene microporous membrane separators (thickness 12 μm) to form a laminate, and this laminate was placed inside an aluminum laminate sheet casing. Subsequently, in an argon box with a dew point temperature of -100 to -50°C, 1 g of non-aqueous electrolyte was injected into the casing using a pipette, and the casing was left standing in a pressure-resistant case. The case was then depressurized to 0.1 atmospheres or less using a vacuum pump, and the depressurized state was maintained for 5 minutes to perform the vacuum impregnation process. After that, the pressure was returned to atmospheric pressure, the casing was sealed, and a laminate type non-aqueous secondary battery (hereinafter referred to as the battery sample) was fabricated. During the vacuum process, the battery weight was measured before and after the vacuum process, and the difference in weight was considered the amount of non-aqueous solvent in the electrolyte that evaporated. Furthermore, the weight ratio of the amount of liquid evaporated to the amount injected was calculated, and this value was evaluated as the volatility (%) of the vacuum process for each electrolyte. The evaluation results of ionic conductivity (μ) and vacuum process volatility (v) for each electrolyte composition are summarized in Table 1, and their compatibility was further evaluated as μ / v.

[0130] (3-2) The initial performance of the electrolyte after conditioning and the charge / discharge vacuum process was evaluated using the following procedure. The ambient temperature of the battery sample prepared in (3-1) was set to 25°C, and it was charged with a constant current of 0.025C until the battery voltage reached 3.6V. After that, constant voltage charging was continued while maintaining the battery voltage at 3.6V until the current decreased to 0.02C. A 10-minute rest period was taken after charging, and then it was discharged to 2.0V with a constant current of 0.1C. Charge and discharge were performed using the ACD-01 charge / discharge device (product name) manufactured by Asuka Electronics Co., Ltd. and the PLM-63S constant temperature bath (product name) manufactured by Futaba Scientific Co., Ltd. Subsequently, the ambient temperature was set to 25°C, and the batteries were charged to 3.6V with a constant current of 0.2C. Constant voltage charging was then performed while maintaining the voltage until the current decreased to 0.05C. After a 10-minute pause, constant current discharge was performed at 0.2C to 2.0V, and the discharge capacity (Wh%) relative to the design capacity was evaluated for each electrolyte. Here, the design capacity calculated from the electrode specifications of the battery samples prepared for the characteristic evaluation of the electrolytes was approximately 0.99Wh.

[0131]

[0132]

[0133] The non-aqueous electrolyte according to this disclosure preferably has an ionic conductivity of 13 mS / cm or higher, more preferably 14 mS / cm or higher, and even more preferably 15 mS / cm or higher. Examples 1 to 6 contain mononitrile as component (a) and 1,2-diethoxyethane or 1,2-dimethoxyethane, which are chain ethers, as component (b), resulting in an ionic conductivity of 14 mS / cm or higher for the electrolyte. Examples 7 and 8 contain a chain carboxylic acid ester as component (b), resulting in an ionic conductivity of 13 mS / cm or higher. Furthermore, regarding the compatibility evaluation value μ / v calculated by the above evaluation in this disclosure, the examples tended to show higher compatibility than the comparative examples while maintaining a high conductivity of 13 mS / cm or higher. In the case of Comparative Examples 1 to 6, where either component (a) or (b) is not included, or neither is included, either the ionic conductivity or the vacuum process resistance is impaired. Furthermore, in electrolytes with an ionic conductivity below 13 mS / cm, the initial capacity tended to decrease relative to the design capacity. Also, in this evaluation, charge-discharge tests were not performed when the volatility exceeded 2.0% (indicated by × in the table).

[0134] Examples 9-22 and Comparative Examples 7-10: Examples of embodiments in which the electrolyte, adjusted to have a conductivity of 13 mS / cm or higher, achieves both conductivity and vacuum process resistance while also improving stability under high-temperature conditions, will be described in detail below.

[0135] As described in "(1) Preparation of Non-Aqueous Electrolyte" above, under an inert atmosphere, various non-aqueous solvents containing components (a) and (b) are mixed in predetermined volume composition ratios, and lithium bis(fluorosulfonyl)imide (LiFSI) and LiPF ６ Dissolve 1 M and 0.3 M of each, and add a predetermined amount (by weight) of additive to the total volume of the electrolyte to prepare a non-aqueous electrolyte. After preparation, an ion conductivity meter CM-41X (product name) and an ion conductivity measuring cell CT-58101B (product name) manufactured by DKK Corporation were inserted into the container holding the electrolyte, and the ion conductivity of the electrolyte at 25°C was measured. Subsequently, the positive electrode and negative electrode were prepared as described in "(2) Preparation of Non-Aqueous Secondary Battery" above.

[0136] (3) Fabrication and evaluation of non-aqueous secondary batteries (3-1) Fabrication of laminate sheet type non-aqueous secondary battery In a dry room with a dew point temperature of -80 to -20°C, the leaded positive electrode and leaded negative electrode, after cutting, were stacked in layers of eight sheets with polyethylene microporous membrane separators (thickness 12 μm) to form a laminate, and this laminate was placed inside an aluminum laminate sheet casing. Subsequently, in an argon box with a dew point temperature of -100 to -50°C, 1 g of non-aqueous electrolyte was injected into the casing using a pipette, and the casing was left to stand in a pressure-resistant case and the case was sealed. The pressure was then reduced to 0.1 atmospheres or less and the reduced pressure state was maintained for 5 minutes to perform a vacuum process to promote impregnation. After that, the pressure was returned to atmospheric pressure and the casing was sealed to fabricate a laminate type non-aqueous secondary battery (hereinafter referred to as the battery sample). During the vacuum process, the battery weight was measured before and after the vacuum process, and the difference in weight was considered the amount of non-aqueous solvent in the electrolyte that evaporated. Furthermore, the weight ratio of the amount of liquid evaporated to the amount injected was calculated, and this value was evaluated as the volatility (%) of the vacuum process for each electrolyte. The evaluation results of ionic conductivity (μ) and vacuum process volatility (v) for each electrolyte composition are summarized in Table 1, and their compatibility was further evaluated as μ / v.

[0137] (3-2) Conditioning and High-Temperature Stability Evaluation The initial performance of the electrolyte after the vacuum process was evaluated using the following procedure. The ambient temperature of the battery sample prepared in (3-1) was set to 25°C, and the battery was charged with a constant current of 0.025C until the battery voltage reached 3.6V. After that, constant voltage charging was continued while maintaining the battery voltage at 3.6V until the current decreased to 0.02C. A 10-minute rest period was taken after charging, and then the battery was discharged to 2.0V with a constant current of 0.1C. The charging and discharging were performed using the ACD-01 charge / discharge device (product name) manufactured by Asuka Electronics Co., Ltd. and the PLM-63S constant temperature bath (product name) manufactured by Futaba Scientific Co., Ltd. Subsequently, the ambient temperature was set to 25°C, and the batteries were charged to 3.6V with a constant current of 0.2C. Constant voltage charging was then performed until the current decreased to 0.05C while maintaining the voltage. After a 10-minute pause, constant current discharge was performed to 2.0V at 0.2C, and the discharge capacity (Wh%) relative to the design capacity was evaluated for each electrolyte. Here, the design capacity calculated from the electrode specifications of the battery sample prepared for electrolyte characteristic evaluation was 0.99Wh. Furthermore, the volume of the aforementioned battery sample was measured using a hydrometer (MDS-300, Alpha Mirage Co., Ltd.) to evaluate the initial volume. Next, the ambient temperature was set to 50°C, and the batteries were charged to 3.6V with a constant current of 1C. Constant voltage charging was then performed until the current decreased to 0.05C while maintaining the voltage. After a 10-minute pause, constant current discharge was performed to 2.0V at 1C. This charge-discharge cycle was repeated 100 times to conduct a high-temperature test, and the discharge capacity at the 100th cycle was measured. Subsequently, volume measurements were performed again, and the post-test volume was evaluated. The expansion volume of each battery sample was evaluated from the difference between the initial volume and the post-test volume, and this was defined as the gas volume.

[0138]

[0139]

[0140] Examples 9 to 22 all exhibited high conductivity, with a conductivity of 13 mS / cm or higher. Furthermore, when both component (a) and component (b) were present and the mixing ratio parameter P fell within a predetermined range, the compatibility score calculated from conductivity / volatility tended to be 7 or higher. In addition, the amount of gas in the high-temperature test was preferably 80% or less, more preferably 70% or less, and particularly preferably 50% or less, with Comparative Example 7 set as 100% (reference). Examples 9 to 20 all had a gas amount of 80% or less. On the other hand, when both component (a) and component (b) were present, with component (b) containing a chain-like carboxylic acid ester, and the volume content of the additive vinylene carbonate fell within a predetermined range, the amount of gas generated tended to be 50% or less. Comparative Examples 7 to 10, where the solvent mixing ratio was outside the predetermined range, all had a gas amount of 100% or more. Therefore, by preparing a solution that contains both component (a) and component (b), and further ensuring that their respective contents and the contents of the additives fall within a predetermined range, conductivity, volatility, and high-temperature stability can be improved.

[0141] The non-aqueous secondary battery disclosed herein is expected to be used not only as a battery for automobiles such as hybrid vehicles, plug-in hybrid vehicles, and electric vehicles, but also as a battery for industrial applications such as power tools, drones, and electric motorcycles, as well as in residential energy storage systems.

Claims

1. A non-aqueous electrolyte comprising a non-aqueous solvent and an alkali metal-containing salt, wherein the non-aqueous solvent contains two or more compounds selected from the group consisting of (a) mononitriles with a molecular weight of 40 to 70 and (b) linear ethers or linear carboxylic acid esters with a molecular weight of 70 to 120, and the total volume content of component (a) and component (b) is 0.05 to 0.80 when the total volume of the non-aqueous solvent is 1.

2. The non-aqueous electrolyte according to claim 1, wherein the non-aqueous solvent contains two or more compounds selected from the group consisting of (a) mononitriles having a molecular weight of 40 to 70 and (b) linear carboxylic acid esters having a molecular weight of 70 to 120, and the (b) component contains at least one carboxylic acid ester selected from the group consisting of methyl acetate, methyl propionate, ethyl acetate, ethyl propionate, propyl propionate, isopropyl propionate, methyl isobutyrate, and ethyl isobutyrate, and the total volume content of the (a) component and the (b) component is 0.05 to 0.80 when the total volume of the non-aqueous solvent is 1.

3. The non-aqueous electrolyte according to claim 1 or 2, wherein the non-aqueous solvent comprises at least acetonitrile as component (a).

4. The non-aqueous electrolyte according to claim 1 or 2, wherein when the total volume of the non-aqueous solvent is 1, the volume content of component (a) and component (b) is 0.05 < Va < 0.4 and 0.05 < Vb < 0.

045.

5. The non-aqueous electrolyte according to claim 1 or 2, wherein the non-aqueous solvent satisfies 0.04 < 0.3 × Va + 0.09 × Vb, where Va and Vb are the respective volume contents of component (a) and component (b) when the total volume of the non-aqueous solvent is 1.

6. The non-aqueous electrolyte according to claim 1 or 2, wherein the non-aqueous electrolyte further comprises (c) vinylene carbonate, and the non-aqueous solvent satisfies (1 + Va + Vb × 0.33) × 0.03 ≤ Vc, where Va, Vb, and Vc are the respective volume contents of component (a), component (b), and vinylene carbonate when the total volume of the non-aqueous solvent is 1.

7. The non-aqueous electrolyte according to claim 1 or 2, wherein the non-aqueous electrolyte further comprises (c) vinylene carbonate, and the non-aqueous solvent satisfies the following conditions: when the total volume of the non-aqueous solvent is 1, the volume content of component (a), component (b), and (c) vinylene carbonate are Va, Vb, and Vc, respectively, Vc ≤ (1 + Va + Vb × 0.33) × 0.

061.

8. The non-aqueous electrolyte according to claim 1 or 2, wherein the non-aqueous solvent comprises a chain-like carboxylic acid ester having a molecular weight of 80 to 110 as component (b), and the chain-like carboxylic acid ester comprises at least methyl propionate.

9. The non-aqueous electrolyte according to claim 1, wherein the non-aqueous solvent contains two or more compounds selected from the group consisting of (a) mononitriles having a molecular weight of 40 to 70 and (b) linear ethers having a molecular weight of 90 to 120, and the total volume content of component (a) and component (b) is 0.05 to 0.

80.

10. The non-aqueous electrolyte according to claim 1 or 9, wherein both component (a) and component (b) have a boiling point of 75°C to 130°C at atmospheric pressure.

11. Both component (a) and component (b) have a density of 0.7 to 0.92 g / cm³ at room temperature. ３ The non-aqueous electrolyte according to claim 1 or 9.

12. Let Ti be the boiling point (°C) of each component of component (a) and component (b), and Vi be the volume content of each component in the non-aqueous solvent, and [Vi × (145 / Ti)] apply to all components of component (a) and component (b). ２ The sum of ] is P: P = Σ[Vi × (145 / Ti)] ２ The non-aqueous electrolyte according to claim 1 or 9, wherein when ] 0.4 < P < 2.

35.

13. Density (g / cm³) of each component of (a) and (b) ３ A non-aqueous electrolyte according to claim 1 or 9, wherein the electrolyte is ρi and its boiling point (°C), and contains at least one component whose Ti is between 80 and 95, and all of the components whose Ti is between 80 and 95 have a viscosity of 60 ≤ (Ti × ρi) ≤ 75 and a viscosity at room temperature of less than 0.5 mPa·s.

14. Density (g / cm³) of each component of (a) and (b) ３ A non-aqueous electrolyte according to claim 1 or 9, wherein the electrolyte is ρi and the boiling point (°C) is Ti, and the Ti is greater than 95 to 130, and all of the components with Ti between 95 and 130 have a Ti of 75 < (Ti × ρi) ≤ 105.

15. If Ti is the boiling point (°C) of each component (a) and component (b), and Vi is the volume content in the non-aqueous solvent, then for both components, 0.01 < Vi < (Ti / 135) ２ The non-aqueous electrolyte according to claim 1 or 9.

16. The non-aqueous electrolyte according to claim 1 or 9, wherein the non-aqueous electrolyte comprises acetonitrile as component (a) and 1,2-dimethoxyethane, 1,2-diethoxyethane, or a combination thereof as component (b), and all components other than the non-aqueous solvent have a boiling point of 95°C or higher.

17. The non-aqueous electrolyte according to any one of claims 1, 2, and 9, further comprising vinylene carbonate, ethylene sulfite, or a combination thereof.

18. A non-aqueous lithium-ion secondary battery comprising: a positive electrode having a positive electrode active material layer containing lithium iron phosphate on one or both sides of a positive electrode current collector; a negative electrode having a negative electrode active material layer containing graphite on one or both sides of a negative electrode current collector; a separator; and a non-aqueous electrolyte according to any one of claims 1, 2, and 9.

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